The present invention relates to a vacuum switching apparatus having a function of breaking a large current.
In general, a power receiving/transforming apparatus receives power by a breaker and a disconnector; transforms the power voltage into a voltage suitable for a load by a transformer; and supplies the power thus voltage-transformed to the load. Upon maintenance and inspection of a power receiving/transforming apparatus, in order to keep or ensure the safety of an operator, a breaker is turned off and then a disconnector is turned off for preventing power from being applied again from the power supply side, and further an earthing or grounding switch is turned on to allow remaining charges and an induction current on the power supply side to flow on the earthing side. As one example of a power receiving/transforming apparatus, a gas insulation switching apparatus disclosed in Japanese Patent Laid-open No. Hei 3-273804 is configured such that a breaker, a disconnector, an earthing switch, and a current transformer are individually prepared and are stored in a unit chamber filled with an insulating gas. As another example of a power receiving/transforming apparatus, a switching apparatus disclosed in Japanese Patent Laid-open No. Hei 9-153320 is configured such that it includes a means of stopping a movable conductor 19 at four positions, specifically, a closing position Y1, an opening position Y2, a disconnecting position Y3, and an earthing position Y4 or stopping the movable conductor 19 at three positions, specifically, at the closing position Y1, disconnecting position Y3, and earthing position Y4, to thus build-up three functions of the breaker, disconnector and earthing switch or two functions of the disconnector and earthing switch in a vacuum bulb.
The above-described former vacuum switching apparatus, in which the breaker and disconnector are individually arranged, has a problem in enlarging the size of the apparatus, and has another problem in making the usability poor and causing the possibility of misoperation of an operator because a series of breaking and disconnecting operations upon maintenance and inspection cannot be continuously performed.
The above-described latter vacuum switching apparatus, in which the breaker and disconnector are built-up in one vacuum vessel, has a problem in that in makes the operating mechanism complicated. In a vacuum breaker, there is specified a between-electrode opening distance most suitable for breaking a large current. If the between-electrode opening distance is excessively large, a region in which metal particles released from both electrodes are diffused increases, whereby insulators around the electrodes are contaminated, thereby reducing the insulating performance of a vacuum bulb. Moreover, since the arc length increases, it makes the behavior of the arc unstable, tending to reduce the breaking performance. Conversely, if the between-electrode opening distance is excessively small, the electrodes cannot withstand a transient recovery voltage applied between the electrodes after breaking, causing dielectric breakdown, thus, making breaking impracticable. In view of the foregoing, the prior art switching apparatus must be configured to complete the breaking operation in a state in which the movable conductor is stopped once at a suitable opening position, and then to perform the disconnecting operation separately from the breaking operation. This configuration causes an inconvenience in complicating the operating mechanism.